1. Field of the Invention
The present invention relates to spindle motors for driving the rotation of magnetic disks, optical disks, and the like; information recording and reproducing apparatuses; and hydrodynamic bearings used in the spindle motors and the like.
2. Description of the Related Art
Hydrodynamic bearings, having better rotation accuracy and also quietness than ball bearings, are being put to use in place of the ball bearing devices conventionally used as bearings for the spindle motors of hard disk devices and the like.
In recent years, furthermore, as hard disk devices have become standard equipment in laptop personal computers, and in addition, are seeing increasing levels of use in portable music players and cellular phones, factors such as thinner and more compact designs, lower power consumption, increased shock resistance, and increased lifespan are in demand.
Constraints are readily placed on axis direction dimensions in line with efforts to achieve thinner and more compact designs. As a result, how best to guarantee radial bearing dimensions in order to ensure the required levels of bearing angular stiffness has been a problematic issue. With regard to increasing lifespan, furthermore, how best to ensure a large oil reservoir of the bearing oil within limited bearing dimensions has been a problematic issue. And with regard to shock resistance, it is necessary to prevent the occurrence of oil leakage upon being exposed to shock. Accordingly, the reliability of the bearing device cannot be allowed to decrease with efforts to achieve thinner and more compact designs or increased lifespan.
A range of proposals have been put forth as a means of addressing these market requirements. For example, in some inventions, as shown in FIG. 10 (see U.S. Pat. No. 7,059,773), an equalizing volume 102 is formed on an outer peripheral surface of a cylindrical bearing sleeve 101, a covering cap 104 having a spacer 103 is disposed on an upper end face of the cylindrical bearing sleeve 101, and thereby a connecting channel 106 is formed between the covering cap 103 and a bearing gap 105. Furthermore, a re-circulation channel 107 is provided. In addition, the covering cap 104 is provided with a hole 108 on a side surface. The hole 108 is used when injecting a lubricant 109 following bearing assembly and is formed with a sufficiently small size that the lubricant 109 will not be thrown off as a result of shock or the like.
In the aforementioned bearing construction, the lubricant 109 moves inside a circulation channel including the bearing gap 105 and the re-circulation channel 107, eliminating imbalance in the internal pressure inside the bearing. In addition, the equalizing volume 102, also constituting an oil reservoir, is connected to the bearing gap 105 via the connecting channel 106, and is capable of supplying a vaporized portion of the lubricant 109 and of absorbing a thermal expansion portion of the lubricant 109 as a result of temperature.
In the construction of the aforementioned U.S. Pat. No. 7,059,773, as the equalizing volume 102, constituting the oil reservoir, can be arranged in parallel with the bearing gap 105, the necessary length of the radial bearing section formed by the bearing gap 105 can be secured, and therefore, the required bearing angular stiffness can be realized while also achieving a thinner and more compact design. In addition, as the equalizing volume 102, constituting the oil reservoir, is formed at an outer peripheral portion of the bearing sleeve 101, sufficient capacity can be secured within a range not affecting bearing performance.
In addition, the configurations disclosed in JP 2006-161988A, JP 2006-170230A, and JP 2006-161967 have been proposed as designs having a large oil reservoir and increased lifespan.